We have constructed a lysogen of a lambda derivative in which the prophage is flanked by two genes (lc and ompC) which code for outer membrane porin proteins of E. coli K-12. Induction of this lysogen leads to phage carrying hybrid porin genes, the N-terminal portion of the gene product being one protein and the C-terminal being another. We will use these hybrid proteins to determine the orientation of the porins in the outer membrane, by using antibody to each end of the protein. We will also characterize both porin genes and the hybrid genes by restriction mapping and DNA sequencing. We will also use the phage carrying hybrid porin genes to construct strains diploid for phage receptor proteins (ompC protein) and use these, with the appropriate phage, to select mutants defective in the biosynthesis and export of porin proteins.